fix(searchbox): update directive prop def
fix(searchbox): update directive prop def

An update to Angular 1.4.9 introduced a regression in ngOfficeUiFabric as explained in #139. This fixes the issue for the `uif-searchbox` directive.

References #139. Closes #143.

ngOfficeUIFabric/ng-officeuifabric,s-KaiNet/ng-officeuifabric,jjczopek/ng-officeuifabric,jjczopek/ng-officeuifabric,s-KaiNet/ng-officeuifabric,andrewconnell/ng-officeuifabric,ngOfficeUIFabric/ng-officeuifabric,andikrueger/ng-officeuifabric,johnmeilleur/ng-officeuifabric,rolandoldengarm/ng-officeuifabric,andrewconnell/ng-officeuifabric,rolandoldengarm/ng-officeuifabric,ngOfficeUIFabric/ng-officeuifabric,s-KaiNet/ng-officeuifabric,ngOfficeUIFabric/ng-officeuifabric,s-KaiNet/ng-officeuifabric,ngOfficeUIFabric/ng-officeuifabric,andikrueger/ng-officeuifabric,johnmeilleur/ng-officeuifabric,andikrueger/ng-officeuifabric,jjczopek/ng-officeuifabric,andikrueger/ng-officeuifabric,rolandoldengarm/ng-officeuifabric,jjczopek/ng-officeuifabric,jjczopek/ng-officeuifabric,andikrueger/ng-officeuifabric,rolandoldengarm/ng-officeuifabric,andrewconnell/ng-officeuifabric,rolandoldengarm/ng-officeuifabric,johnmeilleur/ng-officeuifabric,s-KaiNet/ng-officeuifabric,andrewconnell/ng-officeuifabric,andrewconnell/ng-officeuifabric